Nick F

I likened the 12z EC det to Joe Barstardi's recent bath-tub theory in action, with cold upper air / low heights in Siberia to start the cold season sloshing into N America then sloshing over to the far N Atlantic toward NW Europe, albeit with the usual maritime modification. 18z GFS op initially starts the cold slosh toward the NW Europe before sloshing back to Greenland and N Canada as ridging rebuilds over Northern Europe. Waxing and waning of the GFS/GEFS Northern European +height anomaly in the medium-longer range really doesn't excite me or give me hope for snow in coming weeks I'm afraid, give me the EC bath tub slosh any day. nice to see the hints of wintry precip even in the south next week on 18z though, but we have to look west for this cold and bear in mind that the models are often too cold from that direction at that range.

UKMO looks a marked improvement pro blocking close to the east compared to 12z run yesterday with more troughing/energy undercutting to the SW - similar to GFS and it looks better in this respect than EC at this timeframe Quite a few 00z GEFS members have high pressure centre over Scandi at day 8 We are left with an underwhelming 00z EC det. - but is it dealing with the blocking right? It has been the most progressive / keen to blow way the blocking influence over the UK over recent days, despite strong support from GEFS for blocking holding sway, though we have seen the EPS grow support for the blocking over recent runs.

I think they are well-regarded for tropical forecasting Thank goodness it's day 10! Though all models seem to be singing from the same hymn sheet this morning. Still think we may see changes to the wavelengths around Xmas due to tropical forcing / changes over the NE Pacific.

Desperate times when we start wheeling out the JMA, though I suppose that model has more cred than NOGAPS. The short to medium range we will just have to make the most out of the potential for increasingly colder/drier surface air arriving from near continent late week and next weekend as still advertised by 18z GFS, with return of frosty nights. But there are increasing signs we may see sufficient changes in the upper flow around Xmas to perhaps bring something more interesting ...

With the potential for the trop PV retreating west over Canada because of the +EPO / break down of Aleutian high I mentioned in my last post, certainly feasible for a high to the west as per 18z GFS FI, though equally the high may ridge north over or east of the UK, depending how the wavelengths adjust.

The NOAA prognostic 8-14 day 500mb HGHTS/anomalies bears some resemblance to the 11-15 day 00z EPS 500mb mean below. They both actually advertise a pattern change from day 10 with the removal of the ridge over the Aleutains and replacing it with lower heights and a trough over the Gulf of Alaska and Western Canada (+EPO) - so we actually see the deep cold over northern U.S. and eastern Canada retreat west and a SE ridge develop. This *may* relax the jet downstream over the Atlantic heading NE to allow the Euro high to ridge further north. But we still need more energy/troughing to undercut over SW / S Europe - aka -NAO, something that seems to be increasingly hard to attain in winters these days. But the fact that there is this pattern change upstream indicated, not just by EPS, but GEFS too, plus tropical forcing is pretty active over the maritime continent (SE Asia) despite the incoherent and conflicting MJO forecasts from many models, there is a glimmer of hope that we may see changes later in the month to shake up the stagnant pattern.

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Don't envy you and Tony trying to fathom out how the winter may pan out, as there seems to be a lot of conflicting signals. A weaker than average PV to start winter but is increasing in strength, but even so, there is the question of whether there is a disconnect between the strat and trop atm. The lobe of the PV shifting into Canada and cranking up the jet may not have been easily foreseen back in late November either. The persistence of deep cold over N America over the coming days really has the writing on the wall for our fortunes, so not surprised you have the hunch that the EC/EPS maybe calling correct on a mobile run up to Xmas. And if so, this does really question the credibility of those EC monthly runs with the +ve anomalies to the NE it has shown recently. I'm torn between whether I like the idea of the zonal train taking over, as from a cold and snow potential it favours the north. But the Atlantic storms with their wind, rain and cold and potentially wintry Pm flows would provide more interest for us forecasters to write about compared to the quiet and unexciting anticyclonic conditions close to the east proffered by 00z GFS/GEFS. Though, with the high close to the east or over the UK, there is potential, if the flow buckles and splits with more energy going to southern Europe, that the high may build N and NE across Scandi in a more sustained fashion. But the current upper pattern doesn't favour this outcome in the coming 10 days at least. Would need some increased tropical forcing, i.e. MJO through 7-8-1. to change the upper pattern, but any favourable movement would not impact the upper pattern for us until later in the month anyway. For now the deep cold over N America and the strong jet it drives NE over the Atlantic is dictating our destiny for now.

06z GFS says NO to blocking ... picking up the EC trend our just a rogue progressive run out of the other members?

Despite the progressive pattern painted by the majority EPS members as tweeted by Matt, 00z GEFS still going for a blocked signal, I count 15 out 20 members with anticyclonic synoptics over UK at day 10 Christmas Day now on GFS, and still half of the GEFS members look blocked to me on the 25th F Jury's still out for me on where we are headed toward Xmas given the ECMWF progressive vs GFS more blocked ... though can't see any deep cold coming anywhere near the UK unless some big pattern changes occur ... more likely a chance of a chilly continental feed with high pressure close to the east or NE.

... but unless there is a strong upper flow undercutting that ridge over Scandi ... that high is only ever going to sink south I'm afraid. Too much energy heading NE over the Atlantic due to the steep temp gradient over far north Atlantic beneath the deep cold over NE Canada and Greenland. Really need to weaken or retrograde the deep cold pool upstream over Canada to have a fighting chance of keeping a ridge to our NE.

Hmm, H500 pattern ain't ever gonna look like that by mid month! Pinch of salt needed for the weeklies?

Perhaps veering slightly off topic, and not one for pattern matching, but December 2005 bears some similarities as per GFS in that it was quite an anticyclonic and dry month, November that year was colder than average like this year, both now and then weak Nina to neutral ENSO. But December 2005 had a snowy spell in the east to end the month via a Scandi high - despite the run up to Xmas that year having low pressure to the NW and the Euro slug high in place ...

Could be one of the driest Decembers on record if recent GFS runs came off. EC46 weeklies out and it goes for +ve anomaly to the NE and E and -ve anomaly to the west for week 3, more expansive +ve anomaly to the NE week 4 over Scandi. Must admit, not knowing how well they verify at such long lead times, not sure I have a great deal of faith in them yet.

And there was a westerly QBO that winter as now too. 18z GFS op, only thing of note so far is that the high close enough to east later next week to allow a continental flow bringing slightly chillier conditions towards the east - maxes of 6-7C across eastern England next Thursday

Yep, we're reaching rock bottom with the 12 EC det. this evening, the EC/EPS MJO forecasts pretty incoherent today as well. EC46 may offer light at at the end of the tunnel later ... question is will GFS/GEFS give up the blocked signal or will EC move away from its more zonal outlook. At least there are these differences between the 2 models that hint at uncertainty from the medium range.

Hadn't noticed the new trend of the ens to move out of COD into phase 8, but thanks for highlighting this positive step in the right direction to perhaps shake up the wave patterns later this month to encourage more HLBs again. Still some uncertainties in the tropics, so not holding my breath until we see some solid changes in the NWP.

Slightly envious of my Greek colleague going home for Xmas by the time this happens for SE Europe with regards to the Scandi high, there's only one way that's going with most of the jet energy going over the top, though the upside is that we may see a chillier continental flow tail end of next week as the high to the NE sinks south. with the low heights expanding in the polar regions to our N and NW, it will always be a struggle to sustain a ridge over Nern Europe when there's a split flow, unless there is more energy undercutting the ridge over SW Europe and less in the northern arm.

I think there is a enough uncertainty and spread beyond day 7, not just from the GEFS members, but also the EPS members too, to calm the worries that mild SWlys are here for the long haul. Though not totally discount the worries either. The uncertainty seems to stem with how the models modulate deep cold trop vortices dropping down over Canada and Nern U.S. over the next 10 days and consequently how they handle amplification downstream of these vortices over the N Atlantic. One these vortices drops SE over E Canada next 24hrs - introducing cold continental arctic air south across much of northern, central and western U.S. But it's another, much deeper and colder vortex modelled to drop SE then E over Canada next week which could be causing GFS and EC op differences downstream to the upper flow. 00z ECM det. pulled this vortex E out into the NW Atlantic - flattening the flow, whereas 00z and 06z GFS swing the vortex NE toward Labrador Strait and Greenland, amplifying the flow more downstream over the N Atlantic. Just look at the 500mb vortices over N America heading toward NW Atlantic on 00z EC, and you might see what I mean Against the unfavourable background of weak MJO signal, low AAM, wQBO and deep cold over northern N America driving a strong and zonal jet stream, there does appear to be enough volatility to create some amplification downstream over N Atlantic/Europe ... just a case of whether these ridges will set up favourably to advect colder conditions back to us. There are, at least, favourable hints of cross polar ridging appearing on the models later on too - which could help lower the AO index.

The chart you posted on the left is up to 336hrs (week 2) and the right after 336hrs (week 3) though? Nevertheless week 3 does hint at a southerly tracking jet I guess ...

I don't think you can really infer any likely temperature range for the UK from the chart as it is 500mb height anomalies over a week, though it does suggest NW to SE axis to movement of troughing and weather systems, perhaps, rather than SW to NE as is case next few weeks.

That's the problem, too much zonality ploughing deep into NE Europe in next week to two weeks and then there maybe little deep cold to tap into when the synoptics could become favourable aka week 3 from the EPS. Anyway, there's still a weak flame left in the EPS long range to warm the optimism for the rest of the month.

Wrt to EC46 (weeklies), not completely out, but this is week 3 as a teaser ... H500 +anomalies to the NE this time

GFS getting a complete overhaul in a few years to morph into NGGPS http://www.noaa.gov/media-release/noaa-to-develop-new-global-weather-model

Really is going take something not well-modelled by the ops to change the pattern more favourably, like you say warming/+ve heights working down from the stratosphere. However, the MJO for a while is not looking favourable for sustained trop blocking in our locale, plus the upcoming deep and intense cold sweeping N America will only serve to stoke the fire of the PFJ downstream towards the U.K. Not really surprised the ops are churning out the mundane mobile Atlantic charts with unfavourable MJO, low AAM and slightly strengthening wQBO working against HLB ... for now. maybe the EC46 will give some relief from the op monotony later.